Measurement of Elastic Modulus of the Central Bovine Cornea by Means of Holographic Interferometry. Part II. Results

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Background. The structural and elastic properties of the cornea play an important role in the outcome of corneal refractive surgery. A way to describe the elastic properties is to calculate Young's modulus. The tangent Young's modulus (Elt) represents the first part of the viscoelastic response of the intact cornea due to intraocular pressure increase. Method. The tangent Young's modulus (Elt) of the central cornea of 16 fresh enucleated intact bovine eyes determined from the immediate response was calculated by means of holographic interferometry. The stress was an increase of the intraocular pressure. In 16 eyes the change of intraocular pressure was 10 Pa (group I), starting with an intraocular pressure of 1340 Pa (about 10 mm Hg). In 6 of these 16 eyes there was a second pressure increase of 20 Pa starting at the same intraocular pressure of 1340 Pa (about 10 mm Hg) (group II). Results. The mean value for the Young's modulus in group I was 1.58 x 10s Pa. For group II the Young's modulus was 1.60 x 10s Pa. The difference was not significant. The values for the Young's moduli of the cornea of intact eyes are about 100 times smaller than calculations based on experiments with strips of the cornea. Conclusion. It is necessary to consider the localization of the corneal tissue to avoid influences of corneal hydration or dehydration and to define the existing intraocular pressure if Young's modulus of the cornea is to be calculated.

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